1. Field of the Invention
This invention relates to a cross-talk removal apparatus, which removes cross-talk from adjacent tracks contained in the reproduced signal of a main track based on reproduction signals from the main track and from both adjacent tracks of a data recording medium; and to a data reproduction apparatus that uses the cross-talk removal apparatus when reproducing data from a data-recording medium that has tracks.
2. Description of the Related Art
In the case of a large-capacity data-recording medium such as DVD, there is a problem in that cross-talk from adjacent tracks affects the reproduction signal from the main track being reproduced and causes the reproduction quality to decrease. In order to solve this problem, a cross-talk canceller has gained much attention, in which three light beams are used to simultaneously reproduce three adjacent tracks in order to obtain false cross-talk from the reproduction signals of the adjacent tracks, and then the cross-talk is removed by subtracting this cross-talk from the reproduction signal from the main track.
Normally, the three light beams that are used by the cross-talk canceller irradiate positions at specified intervals along the tangent line of the tracks, so there are time differences in the reproduction signals from each of the tracks. Therefore, before removing the cross-talk, it is necessary to delay the reproduction signals from each of the tracks a specified amount in order to remove the time differences and to bring each of the reproduction signals into phase with each other.
On the other hand, the amount that the reproduction signals of each track is delayed does not always become a fixed value, and changes over time according to the changes in the wavelength of the laser or the characteristics of the data-recording medium. Therefore, by finding an optimum amount of delay for a specified timing and adjusting the delay of the cross-talk canceller, it is possible to compensate for the changes over time of the amount of delay. For example, by detecting the jitter value that corresponds to the reproduction signal, the cross-talk increases simultaneously with the increase in jitter value when the delay amount changes, so the delay amount when the jitter value is a minimum can be set for the cross-talk canceller.
Normally, when reproducing data from a data-recording medium having a very narrow track pitch and on which data have been densely recorded, there is a problem that the cross-talk steadily increases, so the effect of applying the aforementioned cross-talk canceller becomes large. However, in the case of current DVD, the track pitch is somewhat wide, so this steady cross-talk does not become so large. For example, the jitter value of the reproduction signal is affected very little by the cross-talk and the disk noise or interference between code in the tangential direction of the track becomes predominant. Therefore, when adjusting the delay of the cross-talk canceller, it is not possible to find an optimum amount of delay.
On the other hand, even when the steady cross-talk between adjacent tracks is small, the actuator may move due to defects or scratches on the surface of the disk, causing the cross-talk to increase temporarily. If the delay is not properly adjusted when this occurs, the amount of delay of the cross-talk canceller will change, and it becomes impossible to properly remove the cross-talk.